Glycosidase inhibitors from urine of Bombyx mori were isolated and their inhibitory activities on glycosidases were evaluated. Six compounds were isolated by using several ion exchange columns, and their chemical structures were identified by the physicochemical and spectral data. Compound IV, V and VI were identified as 1-deoxynojirimycin, fagomine and 1,4-dideoxy-1,4-imino-D-arabinitol, respectively. Among six compounds isolated, 1-deoxynojirimycin(IV) was the most potent inhibitor on α-glucosidase and β-galactosidase of rat intestine, and its inhibitory activities for trehalase and almond β-glucosidase were relatively weak. Compound V and VI retained a little inhibitory potency toward α-glucosidase and β-galactosidase. Compound II and III, however, have been found to have no effect on all glycosidases tested in this study.